Inline [] operator on one-byte strings.

tests/language/optimized_string_charat_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test optimized [] on strings.
+
+var a = "abc";
+var b = "øbc";
+var c = new String.fromCharCodes([123, 456, 789]);
+
+test_charat(s, i) {
+  return s[i];
+}
+
+main() {
+  Expect.equals("a", test_charat(a, 0));
+  for (var i=0; i<10000; i++) test_charat(a, 0);
+  Expect.equals("a", test_charat(a, 0));
+  Expect.equals("b", test_charat(a, 1));
+  Expect.equals("c", test_charat(a, 2));
+  Expect.throws(() => test_charat(a, 3));
+
+  Expect.equals("ø", test_charat(b, 0));
+  for (var i=0; i<10000; i++) test_charat(b, 0);
+  Expect.equals("ø", test_charat(b, 0));
+  Expect.equals("b", test_charat(b, 1));
+  Expect.equals("c", test_charat(b, 2));
+  Expect.throws(() => test_charat(b, 3));
+
+  Expect.equals(new String.fromCharCodes([123]), test_charat(c, 0));
+  for (var i=0; i<10000; i++) test_charat(c, 0);
+  Expect.equals(new String.fromCharCodes([123]), test_charat(c, 0));
+  Expect.equals(new String.fromCharCodes([456]), test_charat(c, 1));
+  Expect.equals(new String.fromCharCodes([789]), test_charat(c, 2));
+  Expect.throws(() => test_charat(c, 3));
+}